The present invention relates to a track belt for a snowmobile. More particularly, the invention relates to a track belt for a snowmobile, which provides improved high-speed running performance for the snowmobile.
Conventionally, for example as shown in FIG. 10, a snowmobile that runs on snow comprises one or two steering skis 2 provided in the front lower part of a car body 1 and an endless track belt main body (caterpillar) 31 in its rear side.
An output from an engine 4 is transmitted to the track belt main body 31 via an automatic transmission 5 and a wheel sprocket 6. Then, the engine output is transmitted to a snow surface by the track belt main body 31. Reference numerals 7 and 8 respectively denote a suspension rail for the track belt main body 31 and a steering handle.
The track belt main body 31 is constructed, for example as shown in FIG. 11, in a manner that reinforcing woven cloths 3a and 3b are respectively disposed in the outside and inside of a core body 9 composed of an organic fiber cord such as a polyester cord, the core body being disposed along a longitudinal direction of the track belt main body 31, the reinforcing woven cloths 3a and 3b are covered respectively with outer and inner cover layers 11a and 11b which are made of elastic rubber materials or the like and, further, in order to increase surface rigidity of a snow contact surface by reinforcing the track belt main body 31, between the core body 9 and the outer reinforcing woven cloth 3a, a plurality of horizontal rigid members 12 (rods) are buried at specified intervals in the longitudinal direction of the track belt main body 31 and in a cross direction of the same.
In the outside of the outer cover layer 11a, a plurality of traction projections 13 are provided at specified intervals in the longitudinal direction of the track main body 3 and in the cross direction of the same. In the inside of the inner cover layer 11b, a driving projection 14 engaged with a pin of the wheel sprocket 6 is integrally provided at a specified interval with respect to the longitudinal direction of the track belt main body 3.
Concerning the reinforcing woven cloths 10aand 3b provided in the outside and inside of the foregoing conventional track belt main body 31, joined parts thereof on the circumference of the track belt main body 3 are formed to have specified overlapping (overlapping between ends and the other ends of the respective reinforcing woven cloths in the longitudinal direction) in places where the horizontal rigid member 12, the traction projections 13 and the driving projection 14 are not positioned. During operation of the track belt, bending occurs repeatedly in the joined parts. However, because of the improvement in snowmobile track belt performance in recent years, bending fatigue in the joined parts has increased, and such bending fatigue causes failures such as peeling or fracture in the joined parts. Consequently, there was a limit to the improvement in high-speed running performance.
In addition, the existence of the joined parts causes rigidity to be non-uniform on the circumference of the track belt main body 31. Because of such non-uniform rigidity, vibrations are generated in the track belt main body 31, or peeling, fracture or other failures have occurred in the joined parts during high-speed running. Thus, there was a limit to the improvement in high-speed running performance.
The reinforcing woven cloth 3a provided in the outside of the track belt main body 3 functions to protect the core body 9 from external damage and hold the horizontal rigid member. Because of the improvement in snowmobile performance in recent years, however, the reinforcing woven cloth 3a does not appropriately perform the function of holding (protecting) the horizontal rigid member and, during high-speed running, failures such as fracture in the outer reinforcing woven cloth 3a or breaking of the horizontal rigid member 12 have occurred. In order to deal with these problems, strength of the reinforcing woven cloth 3a may be increased by increasing its thickness. But such an increase in strength may cause increases in the weight of the track belt main body 31 and rolling resistance. Thus, for the conventional structure, there was a limit to the improvement in snowmobile high-speed running performance.